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Go Back   SailNet Community > On Board > Gear & Maintenance > Engines > Diesel
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Diesel This is a forum dedicated to diesel engines and their applicable accessories.


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Old 02-20-2010
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Overheated Diesel -- What Damage to Look For?

I overheated my 1980 Volvo MD7A yesterday -- I think the raw water intake clogged with debris I'm not totally sure yet. But whatever happened, it happened suddenly. Engine was running fine then it sounded different and the temperature gauge was pegged in the red. I shut down as soon as I noticed the problem and got a tow back in, but the engine was probably overheated for say 5-10 minutes prior to shutdown. There was a little smoke in the engine bay.

What kind of damage should I look for now in the engine? I'm going to go through the cooling system and clean it out/replace impeller etc. but I'm more worried about bigger issues ... any thoughts?
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Old 02-20-2010
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Its a crap shoot...anything form lucking out and nothing happening to a cracked/warped head and or melted pistons cracked rings and scored cylinder walls.

Do your investigation and try and find the cause first...bad impeller etc....and during that investigation check your cooling system for any trace of oil ...and your oil system for any trace of water a good sign right off the bat of either a head gasket or cracked head....BUMMER!

First you will want to install a new thermostat never trust one that has been subjected to an overheating...its cheap insurance.

Then if it was my engine I would pull the glow plugs and spin the engine to see if any water were in any of the cylinders...you wont harm a rod if the water has someplace to go if indeed you took out a head gasket or cracked a head and its letting water into one or more cylinders.

If all is good and you corrected any cooling system blockage...Put the Glow plugs back in and I would try and start her with out the heat exchanger cap on.....check for any bad sound from your engine if it sounds bad shut it down...BUMMER..Piston problums....If it sound good immediately monitor your exhaust for both proper cooling water flow and steam ....If there is steam comming out you have a head gasket or a cracked/ warped head...BUMMER...if not go to the next step your not in the clear yet.

Let the engine come up to operating temp...once the thermostat is opened peer into your heat exchanger...if it has gas bubbles, a funny smell or is violently rolling...You have a blown head gasket or a cracked head...BUMMER!...If all is well go to the next step your not out of the woods yet.

Put the cap back on the heat exchanger and put a load on the engine for 10 or 15 min...you can do this right at the dock in gear with good dock lines...recheck your exhaust for any steam and your oil breather for steam or water condensation...if all is good you are a lucky man...Go sailing with caution for a while one eye glued to the temp guage and your Tow boat policy paid up..check your engine fluids regularly for the first few days of use...if all is well change oil and take a sigh of relief you lucked out.

It may use a little more oil and be harder starting then it use to with a tint of blue smoke out the exhaust..if so you scored the cylinder walls a little and have lost some compression..aging the engine by 2500 hours or so...BUMMER!...not the end of the world so still count your self lucky.
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Last edited by Stillraining; 02-20-2010 at 11:27 PM.
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Old 02-21-2010
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Can not add to previous follow sr advice.marc
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Old 02-21-2010
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Before starting the engine, it would probably be worthwhile to change the oil and check the condition of the oil. Water intrusion into the engine will often leave the oil looking "milky".
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Old 02-21-2010
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The advice above is very good. I just wanted to add some encouragement before you tear into this that engines like the md7a are actually pretty tough so don't despair until you actually find a problem. I have worked on a lot of overheated engines and it is shocking to me how often we can't find any problems and it runs just like it did beforehand.
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Old 02-21-2010
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OK great tips thanks, we will see how it goes. Will suck if I have major issues but right now I'm just happy there wasn't a fire and I was able to make it back to my home dock easily.
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Old 02-23-2010
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Quote:
Originally Posted by klem View Post
....don't despair until you actually find a problem.
I agree.

And to borrow kelm's idea:

I have overheated my engine altogether too many times, and it is shocking to me how often we can't find any problems and it runs just like it did beforehand.

If you catch it right away, that helps. So many things can happen: intake debris, we lost our coolant from a hidden hose breaking to the hot water heater under the galley sole, the old I forgot to open the thru hull (only once in 13 years, so far!), the old M25 alternator bracket broke, you name it, we've had overheats.

Engine is still smilin' back at me!
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Old 03-03-2010
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I would also look at the exhaust side. Hotter than normal gases exited the heat exchanger it could do damage to any plastic or rubber components. i.e. exhaust tubing and muffler.
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Old 03-03-2010
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Overheating

Stillraining gave a lot of good information and advice but I thought I'd add just a bit here. Had a 2GMF Yanmar on my old Hunter 31 that overheated a few times and here is what I learned:
1. DO NOT IMMEDIATELY SHUT DOWN THE ENGINE UNLESS YOU REALLY HEAR SOME BAD (GRINDING) NOISES. Remember, when all internal combustion engines are shut down, the core temperature actually RISES (known as "heat soakback)! Why? Think of why you really start to sweat when you first get off a bike or complete a run. What little cooling you may have had is now gone. What you should do is reduce power to idle and wait a minute or two, then shut it down. That will allow the block to cool naturally and dramatically reduce heat soakback. You can do even more damage to the engine by immediately shutting down an overheated engine!
2. Start at the intake seacock and work your way all the way through the engine to the water lift muffler to determine the reason for the overheating. If there is a problem in the SW cooling side, you will see a drop in water flow out the exhaust. The primary culprits are: debris in the intake, clogged SW filter, bad impeller, clogged heat exchanger and a clogged mixing elbow. I'd take my time and work my way one step at a time. I had a situation once when I'd changed the intake hose on the "vaccum" SW side from the filter to SW pump. Used the wrong kind of hose and every time I ran the engine higher than 1500 rpm, the hose collapsed and the engine overheated. When I shut it down to check the problem, couldn't find anything wrong! Had a mechanic take a look and he figured it out in about 5 seconds. Best $50 I ever spent on that boat!
3. If SW flow is not a problem, it has to be in the FW side and unless you are using too "strong" an antifreeze mixture it is almost certain to be either the thermostat or clogging in the FW side of the heat exchanger.

If you saw smoke in the engine compartment, that isn't a good sign but could be the heat burning off engine paint or something else like that. I would definitely change the oil (and it wouldn't hurt to save a sample and have it analyzed. Matter of fact, that is probably one of the best things you can do since you will get all sorts of valuable info on the condition of you engine) and make sure the oil isn't milky or smells burned. I'd also make sure you don't have any leaking seals (head gasket, etc.) which could have been compromised in a severe overheating.

Good luck.

Tim L.
S/V "Magic" C400
Chesapeake Bay

Last edited by Magic1; 03-03-2010 at 06:39 PM. Reason: gave wrong boat name in narrative. Added info.
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Old 03-04-2010
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If there were no agressive noises just before the engine was shut down, the chances are it'll be OK. If an overheat is going to do any damage, it'll start with pick-up between the rings and the barrels and that makes noise.

Most engines that die from overheating generally don't do any damage to the bottom end (crank and bearings). If there were no agressive sounds before you shut down the next worst enemy is water in the barrels from a blown head gasket or similar- the barrels will corrode irrepairably within a dy or two if not stripped and cleaned.

Good luck.
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